So how exactly, outside of an accountants money saving head, is this "weapon sharing" supposed to work?
One of the examples quoted was giving NATO access to our Challenger 2 tanks. No other NATO nation uses Challenger 2s (indeed the only people apart from the Brits are the Omanis). So what use is a presumably fairly complex bit of kit like a Challenger 2 to a country that has nobody trained, or experienced, in operating it? Yes, no doubt there could be a training package (how long/cost) but the foreign country would still end up with inexperienced crews in a weapon system they have no history of operating, let alone spares, logistics support, etc, etc.....
Lets just drop of a load of F-15s at Coningsby and ask Typhoon pilots to operate them shall we?
If the idea in future is that all of NATO buys the same kit, same rifles, tanks, artillery, aircraft, all to the same mod state, then the idea might have a chance. However, NATO has been trying this for years (they couldn't even agree ultimately on a standard size rifle round!), without success, and how many nations will object to "buying American" in terms of protecting their armament industries, especially as America won't buy non American kit.